Emulsion for surfacing roads



Patented May 12, 1936 UNITED STATES PATENT OFFICE No Drawing.

Application February 24, 1933,

- Serial No. 658,471. In France March 7, 1932 1 Claim. (01. 1341) This invention relates to emulsions for surfacing roads which at the present time are generally constituted approximately as regards one half by bitumens, that is to say natural bitumens or residues of petroleum distillation and as regards the other'half by water charged with a small proportion of an emulsifying agent such as soap, colloid, gelatine, glue or casein.

They usually have the appearance of a dark homogeneous fluid liquid, the solid particles of bitumen in suspension in the water being too fine to be visible to the naked eye.

When laid on the road, these emulsions generally disintegrate in a few minutes, even in five minutes. The solid particles of bitumen join together and agglomerate to a thin film about 1 mm. thick. The water separates and gradually disappears. The bitumen film is formed as soon as the emulsion comes in contact with the road, and therefore on the surface of the latter, without penetrating into the interior of the ground. Moreover the adhesive properties of bitumen are very weak, so that bitumen laid on silex, on paving blocks of sandstone, on smooth roads like certain modern roads (for instance roads of compressed asphalt, of a product called monolastic, and all modern roads made of very fine materials agglomerated with bitumen), does not properly adhere to them and is liable to come off in large slices.

The new emulsion completely remedies these drawbacks. Its disintegration in fact only commences at the expiration of 10-30 minutes or a longer period if desired, so that it penetrates into the joints of the road stone mosaic before disintegrating or breaking up, thus strengthening the road in a downward direction. A pavement can thus be strengthened, the emulsion getting into the sand of the joint and agglomerating it throughout the whole of its depth.

In disintegrating, this emulsion produces a film which adheres in the broken stones, to sandstone paving blocks and to smooth and polished roads such as those made of compressed asphalt, monolastic, etc.

It is chiefly characterized in that in the usual emulsions referred to above about half of the bitumens are replaced by tars of the type called low temperature tars.

This tar must be obtained by distillation of coal carried out in ovens in which the coal is heated gradually and the tars which come out at a temperature between 400 C. and 450 C. with the gas do not come in contact with, or if so only for a short period of time, surfaces heated to a temperature beyond 600 C. which are liable to pyrogenate an excessive proportion of the tar.

These technical conditions are at present fulfilled in the following industrial installations:

1. Ovens for distillation called low temperature ovens, the walls of which are at a temperature not exceeding the desired temperature and 2. More particular ovens for the manufacture of lighting gas with continuous charging, among which may be mentioned those of the Clover- West and Woodall-Duckham type, in which the coal descends slowly in vertical cells, gradually reaches a temperature of 400 C. when it gives off its tar which being carried away by the vertically rising gas comes in contact only to a slight extent and for a very short period of time with the walls of the cell and is not pyrogenated.

It is to be expected that in future many other commercial types of ovens of the same kind will be produced in view 'of the economy of labour obtained with them.

These tars are very different from the coal tars of coke ovens, gas ovens with vertical retorts with intermittent charging or of ovens with horizontal retorts in which the tars, as soon as they leave the coal, meet a wall at 1000 or 1200" C. where they become decomposed and give the classical coal tar. This classical coal tar is chiefly constituted by cyclic hydrocarbons, it contains naphthalene and anthracene and a considerable proportion of free carbon and gives on distillation liquid hydrocarbons of a density from 1000 to 1100 when the boiling point of the tar varies from 200 C. to 360 C. The low temperature tars considered here contain on the contrary only very little or even no naphthalene and very little anthracene, but on the contrary contain parafiins. The liquid hydrocarbons obtained by their distillation have densities from 950 to 1040 when the boiling point of the tar varies from 200 C. to 360 C. The pitch remaining at 360 does not resemble the pitch of the normal coal tar, it contains much less free carbon, is richer in volatile matters and is nearer to petroleum bitumen than to ordinary coal pitch. From the point of view of chemical affinities, the oils extracted from these low temperature tars must be classed in the series of the products of petroleum and not in that of cyclic hydrocarbons.

It has been attempted to add. coal tar to the emulsions hitherto known for the purpose of increasing the surfacing properties, more particularly the plasticity, and for reducing its price.

These attempts failed however for coagulation takes place as soon as the proportion of tar reaches about 20% of the total weight. A granular mass is formed which does not possess any agglomerating power.

On the contrary when part of the bitumen, up to about one half, is replaced according to the invention by low temperature tars, this coagulation need not be feared.

The mixing is done in equal proportions or in 40 parts of one and parts of the other. To make this mixture, the components are liquefied and heated separately to or C. and then mixed together.

This mixture is much more homogeneous, and the subsequent emulsification is greatly facilitated by adding to the bitumen about 3% of its weight of Swedish residuary oil, which is a well known emulsifying agent for the bituminous emulsions, and which is a by-product obtained in the manufacture of sulphite paper pulp. This is a pure vegetal substance derived from the Pinus Silvestris, consisting mainly in a mixture of fatty acids and resin acids in practically equal quantities, and is entirely free from added mineral mixtures.

The mixture can also be rendered more homogeneous and the subsequent emulsification facilitated by adding to the bitumen from 2 to 5% of its weight of medium oil, called also phenolic oil, whether partly neutralized or not, this oil being simply the result of distillation of ordinary tars or of low temperature tars and more particularly of these previously referred to in the specification, taking the fraction which passes over between C. and 240 C. It is the part very rich in phenols and homologues. The addition of this oil to low-temperature tar, more particularly if the latter has been partly distilled as subsequently described, also facilitates the homogenization of the mixture and the subsequent emulsification.

As soon as the tar and bitumen melted at 100 C. are mixed, the mixture is emulsified with Water charged with soap, casein and the like in an ordinary apparatus either with a slow mixer or with a disintegrating mill such as a centrifugal turbine constituted by two discs arranged at a distance of about one tenth of a millimeter apart into which the base material and the water charged with the emulsifying agent are introduced in the centre in order to be discharged at the periphery in the form of emulsions produced by the centrifugal force which breaks up the film of the base product into very fine drops which are immediately coated with the soap suds.

A fluid chocolate colour emulsion is thus obtained the spreading of which in a cold state is very easy.

For special uses which require a surfacing film or skin of great thickness, 5 to 6 cm. for instance, a mixture containing much less water, up to only 12 to 25% of the total Weight, may be prepared in the mixer. This thick mixture must be laid hot, from 45 C. to 80 C. in order to obtain sufficient fluidity. All the relative proportions of low temperature tar and bitumen may be used.-

It has been assumed throughout the preceding description that the low temperature tar was used in the crude state.

This will rarely be the case:

(1) It is advisable to remove the water from the tar.

(2) For applications in depth, it is preferable to remove the volatile parts of the tar which if left in the whole would render it excessively fluid and cause it to penetrate too deeply. This will be the case in new works for penetrating into the stone mosaic of the road and for plugging up surface holes in an old road.

What I claim is:

A stable bituminous emulsion for surfacing of roads, consisting of an emulsified mixture of substantially equal parts by weight of a bituminous base and water, said bituminous base being a mixture of substantially equal parts by weight of a low temperature tar obtained by distillation of coal at a temperature between 400 and 450 C. and a bituminous residue of a petroleum distillation, said bituminous base also containing 2 to 5% by weight of a distillation tar fraction rich in phenols and its homologues distilling ofi between 180 and 240 C. and about 3% of Swedish residuary oil.

ROBERT JOSEPH LACAU. 

